The present invention concerns an encapsulated housing or box for dissipating the heat produced by electrical circuits.
It is known that the present evolution of integrated circuits and hybrid circuits leads to heat dissipation per surface unit which is constantly increasing.
The calories that are thus produced must be evacuated through the intermediary of the housing on which the circuit(s) is(are) assembled.
Therefore, when the junctions of a semi-conductor device in operation are brought to a temperature distinctly higher than the maximum recommended value, a modification of their surface state can be produced which causes irreversible cumulative deterioration or impairment in the characteristics of the device. For certain components made of silicon, the maximal temperature of the junction is about 200.degree. C., but a lower limit is often necessary, particularly in the case of devices encapsulated within a plastic material. Reliability is generally improved through operating at temperatures distinctly lower than the maximal recommanded value.
It is therefore essential that the housing ensures an optimal heat or thermal resistance for it to be adapted to ensuring the evacuation of a high number of calories per surface unit of the substrate (by way of example, heat resistances as low as 1.degree. C./W are desirable).
Integrated circuits are often assembled in modules or units that have a metallic cap. Heat transfer implies a transfer of the integrated circuit towards an external dissipator. When the amount of heat which must be dissipated is relatively small, the metallic cap of the module or unit can be open to air and the bottom of the module or unit connected to the printed circuit through the intermediary of pins. The heat of the integrated circuit is thus dissipated through the substrate of the circuit upon which the module or unit is assembled and through the metallic cap of this unit.
In certain applications, the quantity of heat dissipated in this way is insufficient.
Different devices exist that permit a greater dissipation of heat of integrated circuits .
Therefore, known hermetically sealed boxes or housings are currently available which are constituted by a body or sink or cup into whch are sealed with a borosilicate glass seals that are also made of an Iron-Nickel-Cobalt alloy. A substrate is stuck or brazed to the bottom of the housing which, due to the fact that it is made of an Iron-Nickel-Cobolt alloy, is a poor heat dissipator.
Thereby, the article of IBM TECHNICAL DISCLOSURE BULLETIN vol. 19 no. 8 of January 1977 entitled "Multimode heat sink" describes a device that comprises a heat dissipator provided with recipients. The units, that are assembled on a printed circuit, are disposed inside the recipients. Welding at low melting temperature ensures the connection between the units and the bottom of the recipients. This dissipator can include a water circulation circuit that allows to transfer the heat towards the outside.
But such a device is not modular. Contrary to this, the housing according to the invention allows to realize a circulation network of heat-carrying fluid that allows cooling as close as possible to the pieces and thus avoids the need to reheat the pieces that have remained cold.